An example of a working vehicle, used as a construction machine such as a wheel loader and a forklift, includes one that makes a hydraulic motor operate by oil supplied from a hydraulic pump, and that is configured to run by rotating running wheels provided to an output shaft of the hydraulic motor. In a hydraulic driving device applied to such a working vehicle, oil in a low pressure oil passage is discharged to a motor case of the hydraulic motor through a low pressure selective valve. Further, the oil is discharged (flushed) to an oil tank from the motor case through a tank oil passage. On the other hand, the oil in the oil tank is supplied to the low pressure oil passage by a charge pump. Further, by delivering the oil outside the device, the hydraulic motor is cooled down (see, for example, Patent Literatures 1, 2, and 3).